Acyl carrier protein from Escherichia coli I. Aspects of the solution structure as evidenced by proton nuclear Overhauser experiments at 500 MHz.

The downfield aromatic (6-8 ppm) and upfield ring current shifted methyl regions (1-0 ppm) in the proton nuclear magnetic resonance spectrum of acyl carrier protein (ACP) from Escherichia coli have been examined at 500 MHz by using nuclear Overhauser methods. The data are analyzed in terms of the secondary structural model of Rock & Cronan (1979) [Rock, C. O., & Cronan, J. E., Jr. (1979) J. Biol. Chem. 254, 9778-9785], which suggests the existence of four alpha-helical segments joined by three beta-turns, and a short coil at the C terminus of the protein. Nuclear Overhauser effects among Tyr-71, Ile-69, Ile-72, and His-75 allow refinement of the secondary structure of the C terminus. Nuclear Overhauser effects among Tyr-71, Phe-28, and three Ile's also place stringent limitations on the folding of the four alpha-helices. These data allow the proposal of a tertiary structural model for ACP.